TW201545448A - Over-current protecting circuit and method for providing over-current protecting reference signal - Google Patents

Abstract

An over-current protecting circuit and a method for providing an over-current protecting reference signal are provided, and may be used to a constant power control of a power conversion device. The over-current protecting circuit includes a resistor network, a peak detection unit and a digital-to-analog converter. The resistor network is used for receiving an input voltage and to provide a divided voltage. The peak detection unit receives the divided voltage, and performs a sample and count process for the divided voltage, so as to generate a digital peak value. The digital-to-analog converter performs a digital-to-analog conversion to the digital peak value, so as to provide the over-current protecting reference signal. The over-current protecting reference signal only follows the input voltage to make changes, and the updated over-current protecting reference signal is independent of a turn ratio of a transformer or an output voltage of the power conversion device.

Description

Overcurrent protection circuit and method for providing overcurrent protection reference signal

The present invention relates to an overcurrent protection technique for a power conversion device, and more particularly to an overcurrent protection circuit and a method of providing an overcurrent protection reference signal.

The main purpose of the power conversion apparatus is to convert the high voltage and low stability AC voltage provided by the power company into a low voltage suitable for various electronic devices and has better stability. DC voltage. Therefore, power conversion devices are widely used in electronic devices such as computers, office automation equipment, industrial control equipment, and communication equipment.

1 is a schematic diagram of a conventional power conversion device. The power conversion device 10 includes a rectifier circuit 12, a transformer T, a feedback unit 14, a control circuit 50, and a power switch Q. The rectifier circuit 12 receives the AC voltage AC_IN and rectifies it. Reaction of the AC voltage on the secondary side NS of the transformer T (by the primary side of the transformer T NP, two The coil ratio of the secondary side NS is determined by the rectification of the diode D1 and the filtering of the capacitor C1 to be converted into the output voltage Vout. The feedback unit 14 is configured to receive the output voltage Vout and output a feedback signal Vfb associated with the loading status of the electronic device 40. The control circuit 50 generates an overcurrent protection reference signal Vlimit according to a duty cycle of the feedback signal Vfb, and generates a pulse width modulation signal Vpwm for adjusting the power switch Q by using the overcurrent protection reference signal Vlimit.

When the control circuit 50 performs constant power control, its architecture includes an overcurrent protection circuit 20. The overcurrent protection circuit 20 generates an overcurrent protection reference signal Vlimit according to a duty cycle (referred to as a duty cycle) of the feedback signal Vfb. The aforementioned duty cycle determines the magnitude of the overcurrent protection reference signal Vlimit. Since the aforementioned duty cycle is associated with the output voltage Vout, and the output voltage Vout is again related to the design of the transformer T, that is, the output voltage Vout is related to the coil ratio n. Therefore, it can be understood that the overcurrent protection reference signal Vlimit is related to the output voltage Vout (or the load state of the electronic device 40), and the overcurrent protection reference signal Vlimit is also related to the coil ratio n. In general, under certain extreme operations, the value of the overcurrent protection reference signal Vlimit is very unstable due to a change in the load state or a coil ratio n of the transformer T. Therefore, the overcurrent protection control of the conventional power conversion device 10 is not stable.

In view of this, the present invention provides an overcurrent protection circuit and a method of providing an overcurrent protection reference signal to solve the problems described in the prior art.

The present invention provides an overcurrent protection circuit including a resistor network, The peak detection unit and the first digit to analog converter. The resistor network is used to receive the input voltage and provide a divided voltage. The peak detecting unit is coupled to the resistor network. The peak detecting unit receives the divided voltage, and performs sampling and counting operations on the divided voltage to generate a digital wave peak. The first digital to analog converter is coupled to the peak detecting unit, and performs digital to analog conversion on the digital wave peak to provide an overcurrent protection reference signal.

In an embodiment of the invention, the input voltage is a full-wave or half-wave signal after rectification of the AC voltage, or a DC signal filtered by the capacitor.

In an embodiment of the invention, the peak detecting unit includes a comparator, a flip-flop, a counter, a second digit to analog converter, and a register. The first input of the comparator receives the divided voltage. The data input of the flip-flop is coupled to the output of the comparator. The clock input end of the counter is coupled to the temporary data output end of the flip flop. The input of the second digit to the analog converter is coupled to the output of the counter for providing a peak signal to the second input of the comparator. The input of the register is coupled to the output of the counter, and the output of the register outputs a peak of the digital wave.

In an embodiment of the invention, the peak detecting unit periodically updates the digital wave peak, and when periodically updating the digital wave peak, the period for resetting the peak detecting unit is larger than the period of the input voltage. .

In an embodiment of the invention, the overcurrent protection reference signal is inversely proportional to the peak change of the input voltage. When the peak change of the input voltage goes from a low value to a high value, the change of the overcurrent protection reference signal decreases from a high value to a low value. When the peak change of the input voltage goes from a high value to a low value, the change of the overcurrent protection reference signal rises from a low value to a high value.

The present invention further provides a method of providing an overcurrent protection reference signal, comprising the following steps. Providing a divided voltage according to the input voltage; performing a divided voltage Sampling and counting operations to generate digital wave peaks; and digital-to-analog conversion of digital wave peaks to provide overcurrent protection reference signals.

In an exemplary embodiment of the invention, the step of performing the sampling and counting operations on the divided voltage further comprises periodically updating the digital peak. The period of updating the peak of the digital wave is greater than the period of the alternating voltage.

Based on the above, the overcurrent protection circuit and the method for providing an overcurrent protection reference signal in the present invention provide an overcurrent protection reference signal according to a peak change of the input voltage. The overcurrent protection reference signal is generated independently of the coil ratio of the transformer and also independent of the output voltage, thereby solving the problems described in the prior art.

It is to be understood that the foregoing general description and claims

10‧‧‧Power conversion device

12‧‧‧Rectifier circuit

14‧‧‧Responsible unit

20‧‧‧Overcurrent protection circuit

40‧‧‧Electronic devices

50‧‧‧Control circuit

110‧‧‧Power conversion device

120‧‧‧Overcurrent protection circuit

122‧‧‧Resistor network

124‧‧‧Crest detection unit

126‧‧‧Digital to analog converter

128‧‧‧ comparator

130‧‧‧Factor

132‧‧‧ counter

134‧‧‧Digital to analog converter

136‧‧‧ register

140‧‧‧ Comparator

142‧‧‧Sampling pulse generator

144‧‧‧Delay unit

146‧‧‧Sampling pulse generator

148‧‧‧Delay unit

150‧‧‧Control circuit

AC_IN‧‧‧AC voltage

C1, C2‧‧‧ capacitor

D1‧‧‧ diode

Dp[0:n-1]‧‧‧ digital wave peak

Fdp[0:n-1]‧‧‧ count value

N‧‧‧ coil ratio

NP‧‧‧ primary side

NS‧‧‧ secondary side

OCP‧‧‧Overcurrent protection signal

RS‧‧‧ sense resistor

R1, R2‧‧‧ resistance

S1, S2‧‧‧ sampling pulse wave

S10, S20, S30‧‧‧ steps

T‧‧‧Transformer

Tac, Tfast, Tupdate‧‧‧ cycle size

Vcs‧‧‧ sense voltage

Vcs_limit‧‧‧Overcurrent protection reference signal

Vfb‧‧‧ feedback signal

Vin‧‧‧Input voltage

Vlimit‧‧‧Overcurrent protection reference signal

Vout‧‧‧ output voltage

Vpwm‧‧‧ pulse width modulation signal

VB‧‧ ‧ voltage divider

Vpeak‧‧‧Crest Signal

The following drawings are a part of the specification of the invention, and are in the

1 is a schematic diagram of a conventional power conversion device.

2 is a schematic diagram of a power conversion device in accordance with an embodiment of the present invention.

3 is a circuit diagram of an overcurrent protection circuit in accordance with an embodiment of the present invention.

4 is a schematic diagram of a waveform in accordance with an embodiment of the present invention.

FIG. 5 is a graph showing changes between an overcurrent protection reference signal and a peak of a divided voltage according to an embodiment of the present invention.

FIG. 6 illustrates a method for providing an overcurrent protection reference signal according to an embodiment of the present invention; Flow chart.

Reference will now be made in detail to the embodiments of the embodiments embodiments In addition, the same or similar reference numerals and components used in the drawings and the embodiments are used to represent the same or similar parts.

2 is a schematic diagram of a power conversion device in accordance with an embodiment of the present invention. Referring to FIG. 2, the power conversion device 110 includes a rectifier circuit 12, a transformer T, a control circuit 150, a power switch Q, and a sense resistor RS.

The rectifier circuit 12 is configured to receive an AC voltage AC_IN and convert the AC voltage AC_IN to provide an input voltage Vin. That is, the input voltage Vin is a rectified signal of the AC voltage AC_IN. The input voltage Vin can be a full wave or a half wave signal. In another embodiment, the power conversion device 110 may not include the rectifier circuit 12, and the input voltage Vin may directly receive a DC signal similar to that filtered by the capacitor C2.

The transformer T has a primary side NP and a secondary side NS. The first end of the primary side NP of the transformer T is for receiving the input voltage Vin. The first end of the power switch Q is coupled to the second end of the primary side NP of the transformer T. The second end of the power switch Q can be coupled to a ground potential through the sensing resistor RS. The control terminal of the power switch Q is configured to receive a pulse width modulation signal Vpwm provided by the control circuit 50. The secondary side NS of the transformer T is used to provide an output voltage Vout to an electronic device 40 in response to switching of the power switch Q.

Control circuit 150 can include overcurrent protection circuit 120 and comparator 140. The overcurrent protection circuit 120 generates an overcurrent protection reference signal Vcs_limit according to the input voltage Vin, and the manner of generation will be described in detail in the embodiment of FIG. 3 below.

Further, in the present embodiment, the manner in which the overcurrent protection reference signal Vcs_limit is generated is independent of the turn ratio n of the transformer T, and is also independent of the output voltage Vout. When the control circuit 150 performs the constant power control, the comparator 140 can compare the overcurrent protection reference signal Vcs_limit with the sensing voltage Vcs to provide the overcurrent protection signal OCP.

FIG. 3 is a circuit diagram of an overcurrent protection circuit 120 in accordance with an embodiment of the present invention. Referring to FIG. 2 and FIG. 3 together, the overcurrent protection circuit 120 includes a resistor network 122, a peak detecting unit 124, and a digital to analog converter 126.

The resistor network 122 can include resistors R1 and R2 for receiving the input voltage Vin and providing a divided voltage VB. The resistor network 122 can also include other impedance components, and the embodiment does not limit the implementation of the resistor network 122 herein.

The peak detecting unit 124 is coupled to the resistor network 122 and the digital to analog converter 126. The peak detecting unit 124 receives the divided voltage VB, and performs sampling and counting operations on the divided voltage VB, thereby generating a digital wave peak value Dp[0:n-1]. Next, the digital-to-analog converter 126 performs a digital-to-analog conversion on the digital peak value Dp[0:n-1] to provide an overcurrent protection reference signal Vcs_limit.

More specifically, the peak detecting unit 124 includes a comparator 128, a flip-flop 130, a counter 132, a digital-to-analog converter 134, and a register 136. The first input of comparator 128 receives a divided voltage VB. The data input of the flip flop 130 is coupled to the output of the comparator 128. The clock input terminal of the counter 132 is coupled to the temporary data output terminal of the flip-flop 130. The input of the digital to analog converter 134 is coupled to the counter 132 output.

The comparator 128 compares the divided voltage VB with the peak signal Vpeak detected in the previous cycle. During each period of the sampling pulse S2, the flip-flop 130 detects the logic level output by the comparator 128. If the high logic bit criterion indicates that the peak value of the divided voltage VB of this period is higher than the peak of the previous period, then The count of the counter 132 is incremented once, and the count value Fdp[0:n-1] of the N-bit is output. The digit to analog converter 134 performs a digital to analog conversion of the count value Fdp[0:n-1] to provide an analog type of peak signal Vpeak to the second input of the comparator 128. The comparator 128 can compare the divided voltage VB with the peak signal Vpeak again. When the peak signal Vpeak is greater than the divided voltage VB, the counter 132 stops counting. If the value of the divided voltage VB rises, the counter 132 will continue to increase the count value.

The input of the register 136 is coupled to the output of the counter 132, and the output thereof outputs a digital peak value Dp[0:n-1]. The peak detecting unit 124 periodically updates the digital wave peak value Dp[0:n-1], and is used to reset the peak detecting unit 124 when the digital wave peak value Dp[0:n-1] is periodically updated. The period size Tupdate needs to be greater than the period size Tac of the input voltage Vin to ensure that the maximum peak value of the plurality of sine waves can be obtained, wherein Tupdate can be M times Tac.

In addition, the peak detecting unit 124 may further include sampling pulse wave generators 142, 146 and delay units 144, 148. The output of the sampling pulse generator 142 is coupled to the clock input of the flip-flop 130 and the input of the delay unit 144. The output end of the delay unit 144 is coupled to the reset end of the flip flop 130. An output of the sampling pulse generator 146 is coupled to an input of the delay unit 148. The output of the delay unit 148 is coupled to the reset terminal of the counter 132. The sampling pulse waves of the sampling pulse wave generators 142 and 146 are respectively S2 and S1, and the corresponding cycle sizes are respectively Tfast and Tupdate, wherein the cycle size is closed. Is Tupdate>Tac>Tfast.

The peak value of several peak signals Vpeak can be detected during each period of the period Tupdate. The value of the counter 132 is temporarily stored in the register 136, and the counter 132 is reset every cycle size Tupdate to re-compare the divided voltage VB and the peak signal Vpeak.

When the counter 132 is reset, the register 136 continues to hold the previous value of the counter 132. Therefore, the stable overcurrent protection reference signal Vcs_limit can be generated through the digital to analog converter 126.

4 is a schematic diagram of a waveform in accordance with an embodiment of the present invention. Please refer to Figure 4. The peak detecting unit 124 causes the peak signal Vpeak to track the maximum peak value among the plurality of sine waves of the divided voltage VB. The sampling pulse S1 updates the current protection reference signal Vcs_limit every other cycle size Tupdate.

FIG. 5 is a diagram showing a change between an overcurrent protection reference signal Vcs_limit and a peak (Vpeak) of the divided voltage VB according to an embodiment of the present invention. Please refer to Figure 5. The overcurrent protection reference signal Vcs_limit is inversely proportional to the peak (Vpeak) change of the divided voltage VB. When the peak value (Vpeak) of the divided voltage VB changes from a low value to a high value, the change of the overcurrent protection reference signal Vcs_limit decreases from a high value to a low value; when the peak of the divided voltage VB changes (Vpeak) by a high value When the value is low, the change of the overcurrent protection reference signal Vcs_limit rises from a low value to a high value.

On the other hand, the divided voltage VB has a proportional relationship with the input voltage Vin. Therefore, it can be understood that the overcurrent protection reference signal Vcs_limit and the peak change of the input voltage Vin will be inversely proportional. That is, when the peak change of the input voltage Vin changes from a low value to a high value, the change of the overcurrent protection reference signal Vcs_limit is from a high value. The low value decreases; when the peak change of the input voltage Vin changes from a high value to a low value, the change of the overcurrent protection reference signal Vcs_limit rises from a low value to a high value.

Based on the content disclosed in the embodiments of the present invention, a general method for providing an overcurrent protection reference signal can be summarized. More specifically, FIG. 6 is a flow chart showing a method for providing an overcurrent protection reference signal according to an embodiment of the present invention. Referring to FIG. 3 and FIG. 6, the method for providing the overcurrent protection reference signal in this embodiment may include the following steps.

The divided voltage VB is supplied in accordance with the input voltage Vin (step S10).

The sampling and counting operations are performed on the divided voltage VB, whereby the digital wave peak value Dp[0:n-1] is generated (step S20).

Next, digital-to-analog conversion is performed on the digital wave peak value Dp[0:n-1], thereby providing an overcurrent protection reference signal Vcs_limit (step S30).

Further, the step of performing the sampling and counting operations on the divided voltage VB may further include periodically updating the digital wave peak value Dp[0:n-1]. The period length Tupdate of the updated digital peak value Dp[0:n-1] needs to be greater than the period size Tac of the AC voltage AC_IN to ensure that the maximum peak value of the plurality of sine waves can be obtained, wherein Tupdate can be M times Tac .

In summary, the overcurrent protection circuit and the method for providing an overcurrent protection reference signal in the present invention provide the overcurrent protection reference signal Vcs_limit according to the peak variation of the input voltage Vin. The overcurrent protection reference signal Vcs_limit is generated independently of the coil ratio n of the transformer T, and is also independent of the output voltage Vout, thereby solving the problems described in the prior art.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art without departing from the invention In the spirit and scope, the scope of protection of the present invention is subject to the definition of the scope of the appended patent application.

In addition, any of the objects or advantages or features of the present invention are not required to be achieved by any embodiment or application of the invention. In addition, the abstract sections and headings are only used to assist in the search of patent documents and are not intended to limit the scope of the invention.

120‧‧‧Overcurrent protection circuit

122‧‧‧Resistor network

124‧‧‧Crest detection unit

126‧‧‧Digital to analog converter

128‧‧‧ comparator

130‧‧‧Factor

132‧‧‧ counter

134‧‧‧Digital to analog converter

136‧‧‧ register

142‧‧‧Sampling pulse generator

144‧‧‧Delay unit

146‧‧‧Sampling pulse generator

148‧‧‧Delay unit

Dp[0:n-1]‧‧‧ digital wave peak

Fdp[0:n-1]‧‧‧ count value

R1, R2‧‧‧ resistance

S1, S2‧‧‧ sampling pulse wave

Tac, Tfast, Tupdate‧‧‧ cycle size

VB‧‧ ‧ voltage divider

Vcs_limit‧‧‧Overcurrent protection reference signal

Vin‧‧‧Input voltage

Vpeak‧‧‧Crest Signal

Claims (10)

An overcurrent protection circuit includes: a resistor network for receiving an input voltage and providing a divided voltage; a peak detecting unit coupled to the resistor network, the peak detecting unit receiving the divided voltage Performing a sampling and counting operation on the divided voltage to generate a digital wave peak; and a first digital to analog converter coupled to the peak detecting unit to perform a digital to analog conversion on the digital peak According to, an overcurrent protection reference signal is provided. The overcurrent protection circuit according to claim 1, wherein the input voltage is a full-wave or half-wave signal after rectification of the AC voltage, or a DC signal filtered by the capacitor. The overcurrent protection circuit of claim 1, wherein the peak detecting unit comprises: a comparator, the first input end receives the divided voltage; and a flip-flop, the data input end coupled to the data input end The output of the comparator; a counter whose clock input is coupled to the temporary data output of the flip-flop; a second digit to the analog converter, the input of which is coupled to the output of the counter to provide a peak The signal is applied to the second input terminal of the comparator; and a register is coupled to the output of the counter, and the output terminal outputs the peak value of the digital wave. The overcurrent protection circuit of claim 1, wherein the peak detection unit updates the digital peak more periodically, and resets the peak detection when the digital peak is periodically updated. The period of the measuring unit is larger than the period of the input voltage. The overcurrent protection circuit of claim 1, wherein the overcurrent protection reference signal is inversely proportional to a peak change of the input voltage: when the peak change of the input voltage changes from a low value to a high value, the overcurrent The change of the protection reference signal decreases from a high value to a low value; and when the peak change of the input voltage goes from a high value to a low value, the change of the overcurrent protection reference signal rises from a low value to a high value. A method for providing an overcurrent protection reference signal, comprising: providing a divided voltage according to an input voltage; performing a sampling and counting operation on the divided voltage to generate a digital peak; and performing the digital peak A digital to analog conversion is provided to provide the overcurrent protection reference signal. The method for providing an overcurrent protection reference signal according to claim 6, wherein the input voltage is a rectified full-wave or half-wave signal of the AC voltage, or a capacitively filtered DC signal. The method for providing an overcurrent protection reference signal according to claim 6, wherein the step of performing the sampling and counting operation on the divided voltage further comprises: periodically updating the digital peak. The method for providing an overcurrent protection reference signal according to claim 8, wherein the period of the peak of the digital wave is updated to be greater than the period of the input voltage. The method for providing an overcurrent protection reference signal according to claim 6, wherein the overcurrent protection reference signal is inversely proportional to a peak change of the input voltage: When the peak change of the input voltage goes from a low value to a high value, the change of the overcurrent protection reference signal decreases from a high value to a low value; and when the peak change of the input voltage goes from a high value to a low value, the The change in the current protection reference signal rises from a low value to a high value.